Duplex radio system



2Sert l15. ,1925. 1,553,625

J. MILLS l DUPLEX RADIO sYs'ru Filed Dec; 24.- 1920 2 sheets-shet 1 fm2A;

Ha "6I sept. 15, 192:5. 1,553,625

J. MILLS DUPLEX RADIO SYSTEM Filed Der. 24, i920 2 sneersneet 2 PatentedSept. 15, 1925.

7 UNIT-Eni: STATES-1;,PATENT OFFICE. f

JOHN MILLS, or WYOMING, .NEW JERSEY, AssIGNoR kTo WESTERN ELECTRICCOMPANY, INCORPORATED, or NEW YORK, N. Y., A CORPORATION or NEW YORK. Y

DUPLEX vRADIO SYSTEM.

Application -lel-December 24, 11920.. Serial No. 432,969.

T all whom it may concern:

Be it known that I, JOHN MILLS, .a citizen of the United States,kresiding at Wyoming, in the county of-Essex,-State of New 6 Jersey,have invented certain newanduseful Improvements 4in -Duplex RadioSystems, of which,-thefollowing is a full, clear,

concise,aiid exact description.

This invention relatesto a duplex rad-io.

10 transmission system.

An object of the invention 1s to provide a means-for duplex carrierqwavetransmission employing :the vsame carrier frequency for both idirections. l

Another Vobject ofthe invention is toprovide a method lof and means yforpreventing side tone interference at ,a receiving station due tosimultaneous reception of the de? sired Signal wave'and the wave fromthe related or local transmitting cir-cuit. f

Further Objects will occur as the description of the invention proceeds,wherein, for example, it `will be shown `that the discriinination soughtisp-independent of the direction of the communicating statioinand alsothat they correspondence f between the balanced andbalancingrwavesissecured in a simple manner fbyderiving them from a thetransmitted and received signals. centralsta'tion may be, in a practicalcase,

the exchange of the local telephone system so that Vany subscriber tothe telephone system can be connected to theradio system, al-

though the arrangements, in general, are equally applicableA totelegraphy. ,Y f i `The conjugate relation of the transmitting andreceiving-circuits.to the common.

line etfectually prevents theoutgoing energy from the common lineentering the receiving circuits. Thecondition Ofuse` of the same high1frequency for the two. directions of transmission reqnirestlhat thereceiving circuits be tuned to thefrequency ofthe waves sent*y out fromthe relatedr or local transmitting unit, and accordingly thesecir- 'hemethod of the invention has applica-- cuits may receive afportion of theenergy sent out from the transmitting unit andl give an undesirableside'tone in the receiver.

-Further, by reasonof the closed higlifrequency VpathV constitutedby thetransmitf ting circuits, transmitting antenna,-receiving antenna,receiving circuits and the circuit connecting the receivingandtransniitting circuits, any imbalance in this connect- The inventionprovides means to avoid suoli effects by preventing the energy of thewaves Aincident on the receiving antenna-fromy the related'ror localtransmitting antenna from owing in the receiving circuits.

tionk of preventing interference between transmitted 'and receivedrsignals f which would otherwise occur in the event of simultaneousoperation ofthe System in both n directions.

The invention contemplatesl balancing out the portion of the transmittedwave that is incidenten therelated or localyrece'iving antenna by rmeansof van'qauxiliary wave simultaneouslyA transmitted therewith. Auxiliaryantennae, which rmay be small In size as compared with the mainantennae,

yare yused to transmit and receive the auxiliary wave and means areprovided at the lreceiving station to equalize and oppose thev twowaves. The normally received wave frointhe distant station isunaffected.` The condition of complete balance requires that the Opposedwaves must be identical in all respects.' This requirement isksatisfied, in

one arrangement of the invention, by usingy -a common f modulatingywavefor the inainy and auxiliary waves vat the transmitting The inivention accomplishes the additional func-4 ing circuit causes a tendencyto-'sing with -atstation, no necessary relation existing between thefrequencies ofthe respective carrier waves, yand effecting, a balancebetween the Adetected modulating components. an alternative* arrangementeffective for components. The requirement to be satislied invthisalternative arrangement is acmodulating characteristics of the opposedwaves mustjbe identical. The desired rc I.telegraph transmission, vthebalance is effected between high frequency modulated.

spects the two arrangements are similar.

The invention provides for the balancing out of the interfering wave atthe receiving station without special regard to the relative directionsof the distant and related transmission stations. Further, thetransmission 'telephone system.l

of the auxiliary wave byradiation results in the advantage, as comparedwith wire transmission, thaty a balance can be more simply and easilyeffected, inasmuch as the effectsof differentialattenuation and of phaseshift are substantially avoided. i Y

For a'further disclosure of the invention,

reference is made to the detailed description which follows, togetherwith the appended vdrawing,`in which Fig. lv shows in schematicform,acircuit arrangement embodying the invention at one of a pair ofsimilarcom-` muiiicating stations. Fig.2 shows a more specific type ofthe system disclosed in Fig. l, and Fig; 3 shows Vthe system of Fig. 2with the circuits `ofthe several elements of the system disclosed indetail.

In the drawing, the reference letters applied to the several parts arechosen with reference to the conventional terms descriptive of theirfunction. For example, amplifiers, detectors, modulators and filtershave been designated, respectively, Vby AM, D,M andF. v A Referring toFig. 1, 1 indicates, generally, a balanced or hybrid coil arrangement ofa well known .type interconnecting the respective outgoing andincomiiiglines2 and 3 with the line L which may lead toa central control stationor to an exchange of a local By the arrangement shown, a localsubscriber, for example, may transmit speech currents over linesL and 2to the modulators M1 and M2, and may simultaneously receive from`receiving antenna Al. l

M1 and M2 are modulators of any type, on the input circuits of whichcurrents of carrier frequencies are impressed by'generators G, and G2,respectively, of convenienttype 1 and size. To insure that the modulatedcarrier waves transmitted by antennae` A, and

A2 areidentical as to their modulation coinponente, thecarrier wavesimpressed on the linput circuits `of the two modulators are modulated bycurrents from thesarne telephone 'line L. To insure the completeseparation of output energy transmitted from the modulators, the carrierfrequencies p hybrid coil.

are chosen widely different. The transmitting station transmits the twowaves with markedly different amounts of rradiated power, since ,antennaA1 is designed to work with the corresponding receiving Vcircuit atthedistaiit station, while antenna- A2 with its associated circuits andapparatus needs Vonly to have sufficient energy capacity to transmitefficientlyto the auxiliary antenna A2 of the local receiving station.

The waves radiated from aiitcnnAl' and A2, hereinafter to be called,respectively, the

main and auxiliary` transmitting antennae,.- (the waves being similarlydesignated and e distinguished) are received respectively-shy main ,and.auxiliaryl receiving antennae A",

'andlAwantenna Alalso receiving the norinally received wave fromadistantqsource.

it is the purpose ofthe invention to combine the main and auxiliarywaves received from the localtransmitting station in suchl manner thatthey neutralize and 'produce no effect in the hybrid coil, whereas 4thenormally received wave from the distant station, which is received byonly *oneA of the receiving circuits, is transmitted afterkdetectionthrough the hybrid coil in the usualv manner; 1 n r A ready-solution ofthe problem is found by producing in t-he two 'waves radiated from thelocal transmitting antennae, modulations having identical frequencies,wave forms and phases. Since-the carrier frequencies are not identicaland, in fact, have no predetermined'orfixedrelation toeach other, aV

'balance must necessarily be effected between the modulating, oraudio,frequencycomponente; To-this end the received waves are detectedV by.detecting tubes or devices D1 y and D2, intheioutput circuits of`whichvwill accordingly appear aywave of audio frequency together with`lhigher frequency waves, `which latter are effectually sup-` pressed bylow pass filtersFL, which permit the audio frequency wavesr topass. The

amplitude of the voice frequency wave derived from the auxiliary antennais, by means of amplifier AMl, caused to be the same as that transmittedto the other antenna, and these two voice frequency waves are finallysuperposedin an opposing sense in the device AM2 which may functionadditionally as an amplifier, as is indicated in the drawing. Thereceived wave from the distant station is detected by the device D, inthe usual manner and isk transmitted through vfilter FL and device AM2to the Although i there have been shown low pass filters betweenthedetecting` tubes andthek amplifier AM2, these filters are not essentialto thev functioning `of the systeinof the invention, and have been addedkmerely tofelimin'ate disturbance in the telephone receivers, .inasmuchas the higher frequencies resulting from detection, may, in

particular cases, depending uponthe relalused throughout the system,the-invention is not dependent 1n any Way on the use of par-v ticulartypes ofmodulating, vdetecting and amplifying devices, and should not becon sidered as so limited l Referrrngnow to the modification illustratedby Fig. 2, which 1s especially adapted for telegraphic= transmission,the systemk shown 'iis seen to have many features in coininon Awith themore general system( illustrated inFig'. 1, thesefeaturesbei-ng'similarly designated, and not requiring 'specialexplanation. "The systemof Fig..2 differs from that of Fig. v1principallyinth'eluse of a common sourceof main and auxiliary carrierWaves toinsu'rethat the frequencies of these Waves have a fixedand-constant relation -to `each other,`and also rthat one shall beamultiple of the other, the two Waves accordingly being readilyconvertible by the use of l-:nownimeans into Waves of the samefrequency.l Y' c The arrangement for deriving the main and auxiliarycarrier Waves consists .of an overloaded repeating tube fed by generatorG. By virtue of abnormal loading, a tube used in this manner can bercaused to function as a harmonicgenerator. A harmonic generator of thistype is described in some detail inl BritishPatent 142,571. cuits forthis, as well Aasthe other elements of the system are shown in Fig. 3,and only brief mention of them Will be made'here.

The output energy from thegenerator HG is divided and deliveredto rthe,modulators lrfl and M2 intwo portions. Filters Fl and F2 are used inorder topinsure that ,current having'lonly kthe desired frequenciesshall tion" `in the circuits of which they form a part. For exan'iple,the frequency of the currents delivered tomodulator `-M2 is preferablymadeV to correspond to the fundamental frequency of the output currentfrom generator LHGr, ivhilefthe current delivered to ymodulator YM1 hasa frequency vcorresponding to the first even harmonic of thisfiuidamental. Since the fundamental frequency of the output currentof'HG is the same as the frequency/of` generator G, an alternativearrangement Would be that in which the input energy to modulator M2 isAtaken directlyfrom the output of generator f1 The` filters `Fl and F2may be of the welll-mourn Campbell type fully described in 'Patent No.1,227,114, patented May 22, 1917. The circuits o'f one form of thisfilter are shown in Fig. 3. The carrier. Waves ob-v tained in :theymanner .described above are modulated in the same manner as in the sys-The cirtemof Fig. 1,-and the modulatedcarrier- Waves Vare radiated fromantennae Aland A2. lngthis system, as Well asin the other,gtheYantennae, both transmitting and receiving, are tuned totheparticularcarrier frequency used. A `i `The modulated carrier Wavestransmitted by the main and auxiliary transmitting` antennae A, and A2are received, respectively,- on main and auxiliary receiving antennaefr', and AgQ rlllie wave received byantenna A', may, in accordance yWithconventional practice, be considered as made upy of three components; anunmodulateld carrier fre-l quency con'ipon'ent having' frequency l),andv the upper and lcWer sidebands having frequcncics respectivelyequal'to P-l-S, and P- S, S being used to representr the frequency ofthe telegraph or other modulating Wavey and P to` represent the carrierfre-r quency. The corresponding frequencies of the Wave received byantenna AQ, are 1/2 P, f

1/2 lll-S, andi/2 P-S. Since thisiniodification einbodiestlie idea of ahigh frequency balance as distinguished from loW or audiok frequencybalance, the vtwo high frequency' Waves must be identical at thebalancing means and this requires that both the modulation frequenciesand thecarrier frequencies shouldbe equal in the tivo Waves. The

` former have been made equalby the use of a common modulating sourceoaf-frequencies. The latterare made equalby thev use in a particular Wayof the detector D3. inthe auxiliary receiving circuit.

According to theory'ivhich is Well understood in the art, the detectingoperation iesults `in afcomplezi Wave consisting of separable componentshaving frequencies,equalto the sum kand difference frequencies of thecurrents impressed on the input of the detector, as Well as othercomponents having frequenciesk which yare y.double the impressedfrequencies. Since currents of frequenciesA 1/ 2 P, 1/2 P-l-S and'g 1D-Sare impressed on the input of detector Di, the output current Willinclude the coniponent currents' of` frequencies P, P-l-S and P-S,P-l-2S and ijf-2S, all having a frequency'comparable ywith frequency l?.The band filter F B is designed` to pass currents of frequencies P,P-,l-S and P- S and ysuppress currents of frequencies P-2S and P-l-2S.Accordingly, the Wave transmitted to amplifier AM, has the form ofthewave transmitted from the antenna A, and received by antenna AQ. ThisWave is amplified by device AMland superposed in device AM2 in lanopposing` sense with the Wave receivedby Al, as has been described withreference to Fig. 1. It should be noted that the system of-Fig. 2j isespecially adapted for a mode'of operationinwvhich there is a constantmodulating frequency asf, for example, in telegraphy, in which ease the.band filter FB is capa-ble ponentis of a double frequency and doublesvwith each passage of the high frequency ci'rcuit,lthe local transmittingand receiving circuits will not sing.

In Fig. V3 there has been shown a detailed circuit arrangement in whichthe system illustrated schematically in Fig. 2 may be embodied. The`circuit details corresponding to the several elements areconventionally shown and do not require further explanation. It shouldbe understood, however, that these circuit arrangements are illustrativeonly, and that any one of the various arrangements commonly usedk isequally adaptable to the system and other amplifying, detecting,generating means, etc., may be used. In this figure, elements aredesignated similarly to corresponding elements in Fig. 2 and aresimilarly arranged, the only exceptions being amplifier AM, and highpass filter FH, which are shown in inverse relation.

It is to be. noted that the two systems shown have in common the idea oftransmitting from the main andauxiliary antennael of the localtransmitting station radically different amounts of power at radicallydifferent frequencies, `the main carrier wave energy being intended fordistant reception, and the auxiliary 'carrier wave energy for nearby orlocal reception, and of balancingv out at the nearby point such ofthemain carrier frequency energy as may be there,V

f received. Although systems to accomplish the purpose sought have beendisclosed in detail, it should be understood 'that the invention isbroadly as expressed above, and accordingly should not be construed aslimited in any way to the specific arrangement shown, but only by theappended claims.

VVhatis claimed is:

l. The method Yof preventing side tone interference in a duplex radiosignaling system which comprises radiating an auxiliary wave ofdifferent frequency from the rmain radiated wav@ and balancing out bysaid auxiliary wave at the local receiving station,

such of the main radiated wave as may be there received.

' A2. The method of preventing side tone interference in a duplexsignaling system which comprises radiating to 'the receiving station awave of the same modulating characteristic as the normally transmittedwave, but having a different carrier frequency, resonantly receivingsaid wave at the receiving station, converting it to a' wave identicalwith the normally transmitted waive, and

terference in` a duplex radio signaling sys` temarranged fornon-directive transmission and reception, which comprises separatelyradiating an auxiliary wave, separately receiving said wave, andbalancing out thereby at the receiving station such portion of theinterfering energy as may befreceived at said station by combining saidauxiliary received wave therewith in an opposing sense. v 1l. The methodof preventingside tone interference at the receiving lstation of a reilated pair of-non-directive transmitting and receiving stations in aduplexradio communicating system whichy consists in non-directivelyreceiving an auxiliary wave at said receivingstation and balancing outthe interfering' wave by combiningr therewith said auxiliary wave.

5. The method of preventing side tone interference in a duplex radiosignaling sys- Vtem which comprisesradiating a main wave modulated inaccordance with signals, radiating an auxiliary modulated carrier. waveof low power and frequency as compared with the main wave-and modulatedin the same manner, receiving said auxiliary wave, detecting the saine,selecting from the detected `wave that component which has the sainefrequency and waveform as the said main wave, and combining in anopposing sense said component amplified to the proper degree with suchportion of the main transmitted wave as may be received at the relatedreceiving station, whereby said last mentioned wave portion iseffectually balanced out. f

' 6. The method of preventing side tone interference at 4the receivingstation of a related pair of transmitting and receiving stations in aduplex radio communicating system which consists in generating a maincarrier wave, generating an auxiliary wave,

said vauxiliary wavelhaving a frequency which is a subharmonic of thefrequency of said main wave, modulating each of said waves in accordancewith signals, resonantly receiving said modulated wave, detecting saidmodulated auxiliary wave, selecting from the rdetected wave thatcomponent which has the same frequency and wave form as the said mainmodulated wave, and

combining in an opposing sense said component, amplified to the properdegree, with such portion of the main modulated transmitted wave as maybe received at the related receiving station, whereby said 4lastmentioned wave portion isfeifectually balanced out. y

7.y A station of a duplex radio system comprising Vin combination, meansfor transmitting a modulated radioV carrier wave, means for radiating anauxiliary wave of different frequency, means for receiving modulatedcarrier waves from a distant station, means for receiving said radiatedauxiliary wave, and means using said radiated auxiliary wave forbalancing out such portion of the normally transmitted wave from thesame station as is incident on said receiving means.

8. In a communicating station of a duplex radio system adapted formodulated carrier wave transmission, the combination with transmittingand receiving circuits for modulated waves, of separate means associatedwith said circuits for transmitting and receiving an auxiliary wavehaving equivalent modulation characteristics, and further meansassociated with said receiving circuit for combining said receivedauxiliary wave in an opposing sense with such portion of the modulatedtransmitted wave as may be there received Vto balance out the latter.

9. In a communicating station of a duplex radio system adapted formodulated carrier wave telephony, the combination with normaltransmitting and receiving circuits for modulated carrier waves, ofmeans associated with said circuits for transmitting and receiving anauxiliary wavey having equivalent modulation characteristics, and

a frequency which is a subharmonic of t-he normal carrier frequencymeans associated with said receiving circuit for converting saidauxiliary wave to a wave identical in frequency and form with thenormally transmitted wave, and means for combining said convertedauxiliary wave in an opposing sense with suchy portion of the normallytransmittedwave as may be received at said receiving circuit. y

10; A communicating station of a duplex radio system provided with meansfor preventing side tone interference comprising a main transmittingantenna, an auxiliary transmitting antenna, means for the radiat` ingfrom said antennae equivalent mo-dula- `tions on two different carrierfrequency waves, the wave having the lower frequency being radiated fromsaid auxlllary antenna,

a receiving antenna, an auxiliary receiving antenna, means in circuitwith one of said last mentioned antennae -to change the carrierfrequency of the wave thereby received to a frequency equivalent to thatreceived by the other receiving antenna, and means for equalizing andopposing the received waves, wherebyv the effect of the wave receivedfrom said main transmitting antenna is effectually balanced out.

11. A communicating station of a duplex t radio system comprising arelated pair of transmitting and receiving stations, the former of whichcomprises in combination, a main antenna, an `auxiliary antenna arrangedto' transmit low power waves and tuned to a lower frequency than saidmain antenna, modulating means in circuit with.

, tivelyto the main and auxiliary transmitting carrier frequencies, avacuum tube device and an amplifying device both in circuit with saidauxiliary receiving antenna and adapted to equalize the frequency andamplitude of the modulated carrier wave received by said auxiliaryreceiving antenna with the corresponding wave in the main receivingantenna circuit, and means for combining said waves in an opposed sense,whereby such portion of the main transmitted wave as may f bereceived onthe main receiving antenna is efectually balanced out.

12. The combination as specified in claim l1, having a detecting meansin circuit with f said combining means whereby the normally receivedwaves may be received and detected. In witness whereof, I hereuntosubscribe my name this 21st day of December, A. D.

i JOHN MILLS

